A cathode ray tube is frequently used to generate images for displays such as televisions (TVS), computer monitors and others. Referring to FIG. 1, an example of a CRT 10 used in Trinitron (trademark) TVS and monitors manufactured by SONY Corporation is shown. The CRT 10 includes an enclosure or tube 12 which houses a color selecting mechanism known as an aperture grille 14 (partially shown for purposes of clarity). The tube 12 includes a front panel 16 having an inner surface which has been coated with phosphor strips arranged in a stripe configuration suitable for providing a color image. The aperture grille 14 is positioned adjacent the inner surface and opposite an electron gun having a cathode assembly 18, prefocusing 20 and main focusing 22 electron lenses, and a convergence deflector 24. In operation, three primary color (red, green, blue) electron beams 26 are emitted from the cathode assembly 18. The electron beams 26 are then converged onto a center axis of the CRT 10 by the prefocusing 20 and main focusing 22 electron lenses. The electron beams 26 then emerge along divergent paths and are deflected by the convergence deflector 24 to converge on the aperture grille 14 so as to form stripes 28 used for forming color images on the front panel 16.
Referring to FIG. 2, a perspective view of the aperture grille 14 is shown. The aperture grille 14 includes a frame 30 which supports a color screening electrode 33 (partially shown for purposes of clarity). The frame 30, which may be fabricated from a resilient material such as steel, includes a first attachment arm 32 which includes a first upright portion 34 having first 36 and second 38 ends and a first bottom edge 37. The frame 30 also includes a second attachment arm 40 which includes a second upright portion 42 having third 44 and fourth 46 ends and a second bottom edge 45. The first 32 and second 40 attachment arms further include first 48 and second 50 base portions, respectively, to form a substantially L-shaped configuration. In addition, the frame 30 includes substantially U-shaped first 52 and second 54 support arms each having first 56 and second 58 support ends. The first 56 and second 58 support ends are attached, typically by welding, to the first 48 and second 50 base portions, respectively, such that the first 32 and second 40 attachment arms and the first 52 and second 54 support arms form a substantially rectangular configuration. Specifically, a first attachment interface 200 is created between the first support end 56 of the first support arm 52 and the first bottom edge 37 of the first base portion 48 of the first attachment arm 32. A second attachment interface 210 is created between the first support end 56 of the second support arm 54 and the first bottom edge 37 of the first base portion 48 of the first attachment arm 32. A third attachment interface is 220 is created between the second support end 58 of the first support arm 52 and the second bottom edge 45 of the second base portion 50 of the second attachment arm 40. A fourth attachment interface 230 is created between the second support end 58 of the second support arm 54 and the second bottom edge 45 of the second base portion 50 of the second attachment arm 40. Typically, the first 34 and second 42 upright portions and the first 48 and second 50 base portions are each 5-7 mm thick.
The color screening electrode 33 includes first 60 and second 62 border portions and a plurality of stripe shaped slits 64 oriented in a substantially parallel configuration. The slits 64 are made by etching elongated sections of a thin sheet of metal to form a plurality of grille tapes 66 which extend between the first 60 and second 62 border portions. In use, the grille tapes 66 are oriented substantially vertically within the CRT 10 such that the electron beams 26 pass through the slits 64 and strike appropriate phosphor strips on the inner surface so as to form a desired color image.
In order to assemble the color screening electrode 33 to the frame 30, pressure is applied to the frame 33 so as to cause the first 32 and second 40 attachment arms to move inward and toward each other. Further, the color screening electrode 33 is stretched such that the grille tapes 66 are taut. The first 60 and second 62 border portions of the color screening electrode 33 are then attached, by welding for example, to the first 32 and second 40 attachment arms, respectively. The pressure on the frame 30 is then released, which causes the resiliency of the frame 30 to urge the first 32 and second 40 attachment arms back to their original position. This places the grille tapes 66 in tension between the first 60 and second 62 border portions, which serves to reduce vibration of the grille tapes 66. Such vibrations are undesirable since they cause misalignments between the electron beams 26 and the phosphor strips, resulting in a degradation of image quality. By way of example, such vibrations may be caused by external forces such as those generated by sound emitted from a speaker attached to a display.
Referring to back FIG. 2, another method utilized for reducing vibration of the grille tapes 66 includes the use of a damper wire 64. The damper wire 64 is stretched across the grille tapes 66 in a transverse direction such that the damper wire 64 contacts and clamps down on the grille tapes 66. By way of example, the damper wire 64 may be fabricated from tungsten and have a diameter of approximately 20 .mu.m. Further, one or more damper wires may be used depending on the size of the color screening electrode 33. A damper wire may be used to reduce vibrations in a CRT having an arcuately shaped front panel, wherein the color screening electrode is also arcuately shaped, or in a flat display CRT, wherein the front panel and thus the color screening electrode are relatively flat. As such, the clamping force exerted by the damper wire on the grille tapes is greater in arcuately shaped CRTs wherein the damper wire is stretched across an arcuately shaped color screening electrode than in a flat display CRT wherein the damper wire is stretched across a relatively flat color screening electrode.
Frequently, nonuniformities known as wrinkles occur in sections of the grille tapes 66 upon completion of the assembly process. Such wrinkles result in undesirable positioning and orientation of the grille tapes 66, thus causing a degradation of image quality. In arcuately shaped CRTs, the damper wire 64 typically exerts a clamping force sufficient to reduce the amount of wrinkling. However, this is only effective in areas wherein the damper wire 64 actually contacts the grille tapes 66. Further, in flat display CRTs having relatively flat color screening electrodes, the clamping force produced by the damper wire 64 is substantially smaller. As a result, the damper wire 64 in these displays are relatively ineffective in reducing the amount of wrinkling of the grille tapes 66.